The estrogen hormone has a broad spectrum of effects on tissues in both females and males. Many of these biological effects are positive, including maintenance of bone density, cardiovascular protection, central nervous system (CNS) function, and the protection of organ systems from the effects of aging. However, in addition to its positive effects, estrogen also is a potent growth factor in the breast and endometrium that increases the risk of cancer.
Until recently, it was assumed that estrogen binds to a single estrogen receptor (ER) in cells. As discussed below, this simple view changed significantly when a second ER (ER-.beta.) was cloned (with the original ER being renamed ER-.alpha.), and when co-factors that modulate the ER response were discovered. Ligands can bind to two different ERs which, in the presence of tissue-specific co-activators and/or co-repressors, bind to an estrogen response element in the regulatory region of genes or to other transcription factors. Given the complexity of ER signaling, along with the tissue-specific expression of ER-.alpha. and ER-.beta. and its co-factors, it is now recognized that ER ligands can act as estrogen agonists and antagonists that mimic the positive effects, or block the negative effects, of estrogen in a tissue-specific manner. This has given rise to the discovery of an entirely new class of drugs, referred to as Selective Estrogen Receptor Modulators or SERMs. These drugs have significant potential for the prevention and/or treatment of cancer and osteoporosis, as well as cardiovascular diseases and neurodegenerative diseases such as Alzheimer's disease.
Bone-resorbing diseases, such as osteoporosis, are debilitating conditions which affect a wide population, and to which there is only limited treatment. For example, osteoporosis affects about 50% of women, and about 10% of men, over the age of 50 in the United States. In individuals with osteoporosis, increased loss of bone mass results in fragile bones and, as a result, increased risk of bone fractures. Other bone-resorption diseases, such as Paget's disease and metastatic bone cancer, present similar symptoms.
Bone is a living tissue which contains several different types of cells. In healthy individuals, the amount of bone made by the osteoblastic cells is balanced by the amount of bone removed or resorbed by the osteoclastic cells. In individuals suffering from a bone-resorbing disease, there is an imbalance in the function of these two types of cells. Perhaps the most well known example of such an imbalance is the rapid increase in bone resorption experienced by postmenopausal women. Such accelerated bone lose is attributed to estrogen deficiency associated with menopause. However, the mechanism of how the loss of estrogen results in increased bone resorption has long been debated.
Recently, investigators have suggested that an increase in bone-resorbing cytokines, such as interleukin-1 (IL-1) and tumor necrosis factor (TNF), may be responsible for postmenopausal bone loss (Kimble et al., J. Biol. Chem. 271:28890-28897, 1996), and that inhibitors of these cytokines can partially diminish bone loss following ovariectomy in rodents (Pacifici, J. Bone Miner Res. 11:1043-1051, 1996). Further, discontinuation of estrogen has been reported to lead to an increase in IL-6 secretion by murine bone marrow and bone cells (Girasole et al., J. Clin. Invest. 89:883-891, 1992; Jilka et al., Science 257:88-91, 1992; Kimble et al., Endocrinology 136:3054-3061, 1995; Passseri et al., Endocrinology 133:822-828, 1993), antibodies against IL-6 can inhibit the increase in osteoclast precursors occurring in estrogen-depleted mice (Girasole et al, supra), and bone loss following ovariectomy does not occur in transgenic mice lacking IL-6 (Poli et al., EMBO J. 13:1189-1196, 1994).
Existing treatments for slowing bone loss generally involves administration of compounds such as estrogen, bisphosphonates, calcitonin, and raloxifene. These compounds, however, are generally used for long-term treatments, and have undesirable side effects. Further, such treatments are typically directed to the activity of mature osteoclasts, rather than reducing their formation. For example, estrogen induces the apoptosis of osteoclasts, while calcitonin causes the osteoclasts to shrink and detach from the surface of the bone (Hughes et al., Nat. Med. 2:1132-1136, 1996; (Jilka et al., Exp. Hematol. 23:500-506, 1995). Similarly, bisphosphonates decrease osteoclast activity, change their morphology, and increase the apoptosis of osteoclasts (Parfitt et al., J. Bone Miner 11:150-159, 1996; Suzuki et al., Endocrinology 137:4685-4690, 1996).
Cytokines are also believed to play an important role in a variety of cancers. For example, in the context of prostate cancer, researchers have shown IL-6 to be an autocrine/paracrine growth factor (Seigall et al., Cancer Res. 50:7786, 1999), to enhance survival of tumors (Okamoto et al., Cancer Res. 57:141-146, 1997), and that neutralizing IL-6 antibodies reduce cell proliferation (Okamoto et al., Endocrinology 138:5071-5073, 1997; Borsellino et al., Proc. Annu. Meet. Am. Assoc. Cancer Res. 37:A2801, 1996). Similar results have been reported for IL-6 with regard to multiple myeloma (Martinez-Maza et al., Res. Immunol. 143:764-769, 1992; Kawano et al., Blood 73:517-526, 1989; Zhang et al., Blood 74:11-13, 1989; Garrett et al., Bone 20:515-520, 1997; and Klein et al., Blood 78:1198-12-4, 1991), renal cell carcinoma (Koo et al., Cancer Immunol. 35:97-105, 1992; Tsukamoto et al., J. Urol. 148:1778-1782, 1992; and Weissglas et al., Endocrinology 138:1879-1885, 1997), and cervical carcinoma (Estuce et al., Gynecol. Oncol. 50:15-19, 1993; Tartour et al., Cancer Res. 54:6243-6248, 1994; and Iglesias et al., Am. J. Pathology 146:944-952, 1995).
Furthermore, IL-6 is also believed to be involved in arthritis, particularly in adjuvant-, collagen- and antigen-induced arthritis (Alonzi et al., J. Exp. Med. 187:146-148, 1998; Ohshima et al., Proc. Natl. Acad. Sci. USA 95:8222-8226, 1998; and Leisten et al., Clin. Immunol. Immunopathol 56:108-115, 1990), and anti-IL-6 antibodies have been reported for treatment of arthritis (Wendling et al., J. Rheumatol. 20:259-262, 1993). In addition, estrogen has been shown to induce suppression of experimental autoimmune encephalomyelitis and collagen-induced arthritis in mice (Jansson et al., Neuroimmunol. 53:203-207, 1994).
As noted above, it had previously been assumed that estrogen binds to a single estrogen receptor (ER) in cells, causing conformational changes that result in release from heat shock proteins and binding of the receptor as a dimer to the so-called estrogen response element in the promoter region of a variety of genes. Further, pharmacologists have generally believed that non-steroidal small molecule ligands compete for binding of estrogen to ER, acting as either antagonists or agonists in each tissue where the estrogen receptor is expressed. Thus, such ligands have traditionally been classified as either pure antagonists or agonists. This is no longer believed to be correct.
Rather, it is now known that estrogen modulates cellular pharmacology through gene expression, and that the estrogen effect is mediated by estrogen receptors. As noted above, there are currently two estrogen receptors, ER-.alpha. and ER-.beta.. The effect of estrogen receptor on gene regulation can be mediated by a direct binding of ER to the estrogen response element (ERE)--"classical pathway" (Jeltsch et al., Nucleic Acids Res. 15:1401-1414, 1987; Bodine et al., Endocrinology 139:2048-2057, 1998), binding of ER to other transcription factors such as NF-.kappa.B, C/EBP-.beta. or AP-1--"non-classcial pathway" (Stein et al., Mol. Cell Biol. 15:4971-4979, 1995; Paech et al., Science 277:1508-1510, 1997; Duan et al., Endocrinology 139:1981-1990, 1998), and through non-genomic effects involving ion channel receptors (Watters et al., Endocrinology 138:4030-4033, 1997; Improta-Brears et al., Proc. Natl. Acad. Sci. USA 96:4686-4691, 1999; Gu et al., Endocrinology 140:660-666, 1999; Beyer et al., Eur. J. Neurosci. 10:255-262, 1998).
Progress over the last few years has shown that ER associates with co-activators (e.g., SRC-1, CBP and SRA) and co-repressors (e.g., SMRT and N-CoR), which also modulate the transcriptional activity of ER in a tissue-specific and ligand-specific manner. In addition, evidence now suggests that the majority of estrogen-regulated genes do not have a classical estrogen response element. In such cases, ER interacts with the transcription factors critical for regulation of these genes. Transcription factors known to be modulated in their activity by ER include, for example, AP-1, NF-.kappa.B, C/EBP and Sp-1.
Given the complexity of ER signaling, as well as the various types of tissue that express ER and its co-factors, it is now believed that ER ligands can no longer simply be classified as either pure antagonists or agonists. Therefore, the term "selective estrogen receptor modulator" (SERM) has been coined. SERMs bind to ER, but may act as an agonist or antagonist of estrogen in different tissues and on different genes. For example, two of the most well known drugs that behave as SERMs are Tamoxifen and Raloxifene. Studies with these two compounds, as well as other SERMs now in development, have demonstrated that the affinity of a SERM for its receptor in many cases does not correlate with its biological activity. Therefore, ligand-binding assays traditionally used in screening for novel ER modulators have not distinguished between tissue-selectivity and agonist/antagonist behavior.
More recently, a second estrogen receptor, ER-.beta., has been identified and cloned (Katzenellenbogen and Korach Endocrinology 138, 861-2 (1997); Kuiper et al., Proc. Natl. Acad. Sci. USA 93, 5925-5930, 1996; Mosselman et al., FEBS Lett. 392, 49-53, 1996). ER-.beta., and the classical ER renamed ER-.alpha., have significantly different amino acid sequences in the ligand binding domain and carboxy-terminal transactivation domains (.about.56% amino acid identity), and only 20% homology in their amino-terminal transactivation domain. This suggests that some ligands may have higher affinity to one receptor over the other. Further, ligand-dependent conformational changes of the two receptors, and interaction with co-factors, will result in very different biological actions of a single ligand. In other words, a ligand that acts as an agonist on ER-.alpha. may very well serve as an antagonist on ER-.beta.. An example of such behavior has been described by Paech et al. (Science 277, 1508-1510, 1997). In that paper, estrogen is reported to activate an AP-1 site in the presence of ER-.alpha., but to inhibit the same site in the presence of ER-.beta.. In contrast, Raloxifene (Eli Lilly & Co.) and Tamoxifen and ICI-182,780 (Zeneca Pharmaceuticals) stimulate the AP-1 site through ER-.beta., but inhibit this site in the presence of ER-.alpha.. Another example has been described by Sun et al. (Endocrinology 140, 800-4, 1999). In this paper, the R,R-enantiomer of a tetrahydrochrysene is reported to be an agonist on ER-.alpha., but a complete antagonist on ER-.beta., while the S,S-enantiomer is an agonist on both receptors.
Furthermore, ER-.alpha. and ER-.beta. have both overlapping and different tissue distributions, as analyzed predominantly by RT-PCR or in-situ hybridization due to a lack of good ER-.beta. antibodies. Some of these results, however, are controversial, which may be attributable to the method used for measuring ER, the species analyzed (rat, mouse, human) and/or the differentiation state of isolated primary cells. Very often tissues express both ER-.alpha. and ER-.beta., but the receptors are localized in different cell types. In addition, some tissues (such as kidney) contain exclusively ER-.alpha., while other tissues (such as uterus, pituitary and epidymis) show a great predominance of ER-.alpha. (Couse et al., Endocrinology 138, 4613-4621, 1997; Kuiper et al., Endocrinology 138, 863-870, 1997). In contrast, tissues expressing high levels of ER-.beta. include prostate, testis, ovaries and certain areas of the brain (Brandenberger et al., J. Clin. Endocrinol. Metab. 83, 1025-8, 1998; Enmark et al., J. Clinic. Endocrinol. Metabol. 82, 4258-4265, 1997; Laflamme et al., J. Neurobiol. 36, 357-78, 1998; Sar and Welsch, Endocrinology 140, 963-71, 1999; Shughrue et al., Endocrinology 138, 5649-52, 1997a; Shughrue et al., J. Comp. Neurol. 388, 507-25, 1997b).
The development of ER-.alpha. (Korach, Science 266, 1524-1527, 1994) and ER-.beta. (Krege et al., Proc. Natl. Acad Sci. USA 95, 15677-82, 1998) knockout mice further demonstrate that ER-.beta. has different functions in different tissues. For example, ER-.alpha. knockout mice (male and female) are infertile, females do not display sexual receptivity and males do not have typical male-aggressive behavior (Cooke et al., Biol. Reprod. 59, 470-5, 1998; Das et al., Proc. Natl. Acad. Sci. USA 94, 12786-12791, 1997; Korach, 1994; Ogawa et al., Proc. Natl. Acad. Sci. USA 94, 1476-81, 1997; Rissman et al., Endocrinology 138, 507-10, 1997a; Rissman et al., Horm. Behav. 31, 232-243, 1997b). Further, the brains of these animals still respond to estrogen in a pattern that is similar to that of wild type animals (Shughrue et al., Proc. Natl. Acad. Sci. USA 94, 11008-12, 1997c), and estrogen still inhibits vascular injury caused by mechanical damage (Iafrati et al., Nature Med. 3, 545-8, 1997). In contrast, mice lacking the ER-.beta. develop normally, are fertile and exhibit normal sexual behavior, but have fewer and smaller litters than wild-type mice (Krege et al., 1998), have normal breast development and lactate normally. The reduction in fertility is believed to be the result of reduced ovarian efficiency, and ER-.beta. is the predominant form of ER in the ovary, being localized in the granulosa cells of maturing follicles.
In summary, compounds which serve as estrogen antagonists or agonists have long been recognized for their significant pharmaceutical utility in the treatment of a wide variety of estrogen-related conditions, including conditions related to the brain, bone, cardiovascular system, skin, hair follicles, immune system, bladder and prostate (Barkhem et al., Mol. Pharmacol. 54, 105-12, 1998; Farhat et al., FASEB J. 10, 615-624, 1996; Gustafsson, Chem. Biol. 2, 508-11, 1998; Sun et al., 1999; Tremblay et al., Endocrinology 139, 111-118, 1998; Turner et al., Endocrinology 139, 3712-20, 1998). In addition, a variety of breast and non-breast cancer cells have been described to express ER, and serve as the target tissue for specific estrogen antagonists (Brandenberger et al., 1998; Clinton and Hua, Crit. Rev. Oncol. Hematol. 25, 1-9, 1997; Hata et al., Oncology 55 Suppl 1, 35-44, 1998; Rohlff et al., Prostate 37, 51-9, 1998; Simpson et al., J. Steroid Biochem Mol Biol 64, 137-45, 1998; Yamashita et al., Oncology 55 Suppl 1, 17-22, 1998).
In recent years a number of both steroidal and nonsteroidal compounds which interact with ER have been developed. For example, Tamoxifen was originally developed as an anti-estrogen and used for the treatment of breast cancer, but more recently has been found to act as a partial estrogen agonist in the uterus, bone and cardiovascular system. Raloxifene is another compound that has been proposed as a SERM, and has been approved for treatment of osteoporosis. ##STR2##
Analogs of Raloxifene have also been reported (Grese et al., J. Med. Chem. 40:146-167, 1997).
As for coumarin-based compounds, a number of structures have been proposed, including the following: Roa et al., Synthesis 887-888, 1981; Buu-Hoi et al., J. Org. Chem. 19:1548-1552, 1954; Gupta et al., Indian J. Exp. Biol. 23:638-640, 1985; Published PCT Application No. WO 96/31206; Verma et al., Indian J. Chem. 32B:239-243, 1993; Lednicer et al., J. Med. Chem. 8:725-726, 1965; Micheli et al., Steroids 5:321-335, 1962; Brandt et al., Int. J. Quantum Chemistry: Quantum Biol. Symposia 13:155-165, 1986; Wani et al., J. Med. Chem. 18:982-985, 1975; Pollard et al., Steroids 11:897-907, 1968.
Accordingly, there is a need in the art for estrogen antagonists and agonists generally, and more specifically for compounds that inhibit cytokines, particularly IL-6, including pharmaceutical compositions containing such compounds as well as methods relating to the use thereof The present invention fulfills these needs, and provides other related advantages.